1. Field of the Invention
The present invention relates to a method of manufacturing a gas sensor, and more particularly, to a simple method of manufacturing a gas sensor having an improved sensitivity and adsorption selectivity with respect to a specific gas.
2. Description of the Related Art
While it is true that scientific developments have improved the quality of human life, the extensive and rapid destruction of nature caused by industrialization and environmental contamination due to increased energy consumption pose a great threat to human beings.
Accordingly, the development of a reliable and highly sensitive gas sensor that can detect and quantify different kinds of harmful gases that can cause air contamination is needed. Presently, gas sensors are widely used in various industries (such as the manufacturing industry, the agricultural industry, the livestock industry, the office equipment industry, the catering industry, and the ventilation industry), crime prevention (alcohol level checking), environment (air contamination surveillance, combustion control), disaster prevention (gas leaking, oxygen deficiency alarm in mines, fire surveillance), medical (gas analysis in blood, anesthesia gas analysis), and the like, and further applications for gas sensors are widening every day.
In general operation, a gas sensor measures the amount of a harmful gas by using the characteristics of changes in electrical conductivity or electrical resistance according to the degree of adsorption of gas molecules. Gas sensors have been manufactured using a metal oxide semiconductor, a solid electrolyte material, or other organic materials. However, gas sensors that use a metal oxide semiconductor or a solid electrolyte material start the sensing operation when the gas sensor is heated to 200-600° C. Gas sensors that use an organic material have a very low electrical conductivity, and specifically gas sensors that use carbon black and an organic complex have a very low sensitivity.
Carbon nanotubes (“CNTs”) have recently drawn attention as new materials that can be applied to various industrial fields due to their high electron emission characteristics and high chemical reactivity. A particular attribute of CNTs is that CNTs are materials that have very large surface areas relative to the volume of the CNTs. Therefore, the CNT is very useful in fields such as the detection of minute amounts of chemical components and for hydrogen storage. A gas sensor that uses CNTs detects harmful gases by measuring the electrical signal (for example, conductance or resistance) that changes according to the electronic property of a gas adsorbed to the CNTs. CNTs, when used in a gas sensor, are advantageous in that sensing operations of the gas sensor can start at room temperature, and sensitivity and speed of response are very high since there is high electrical conductivity in the CNTs when harmful gases such as NH3 or NO2 react with CNTs in the gas sensor.
However, a gas sensor that only uses CNTs has poor selectivity with respect to a specific gas. As a method of supplementing the drawback of a gas sensor that only uses CNTs, metal that has adsorption selectivity with respect to a specific gas can be deposited on CNTs using a sputtering method or a chemical vapor deposition (“CVD”) method. However, this method requires expensive equipment such as a sputtering apparatus or a CVD apparatus, and the manufacturing process of such a gas sensor is also very complicated.